// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "content/renderer/android/disambiguation_popup_helper.h"

#include <stddef.h>

#include <algorithm>

#include "third_party/WebKit/public/platform/WebRect.h"
#include "ui/gfx/geometry/size_conversions.h"

using blink::WebRect;
using blink::WebVector;

namespace {

// The amount of padding to add to the disambiguation popup to show
// content around the possible elements, adding some context.
const int kDisambiguationPopupPadding = 8;

// Constants used for fitting the disambiguation popup inside the bounds of
// the view. Note that there are mirror constants in PopupZoomer.java.
const int kDisambiguationPopupBoundsMargin = 25;

// The smallest allowable touch target used for disambiguation popup.
// This value is used to determine the minimum amount we need to scale to
// make all targets touchable.
const int kDisambiguationPopupMinimumTouchSize = 40;
const float kDisambiguationPopupMaxScale = 5.0;
const float kDisambiguationPopupMinScale = 2.0;

// Compute the scaling factor to ensure the smallest touch candidate reaches
// a certain clickable size after zooming
float FindOptimalScaleFactor(const WebVector<WebRect>& target_rects,
    float total_scale)
{
    DCHECK_GT(total_scale, 0.0f);
    if (!target_rects.size()) {
        NOTREACHED();
        return kDisambiguationPopupMinScale;
    }
    int smallest_target = std::min(target_rects[0].width, target_rects[0].height);
    for (size_t i = 1; i < target_rects.size(); i++) {
        smallest_target = std::min(
            { smallest_target, target_rects[i].width, target_rects[i].height });
    }
    const float smallest_target_f = std::max(smallest_target * total_scale, 1.0f);
    return std::min(kDisambiguationPopupMaxScale,
               std::max(kDisambiguationPopupMinScale,
                   kDisambiguationPopupMinimumTouchSize / smallest_target_f))
        * total_scale;
}

void TrimEdges(int* e1, int* e2, int max_combined)
{
    if (*e1 + *e2 <= max_combined)
        return;

    if (std::min(*e1, *e2) * 2 >= max_combined)
        *e1 = *e2 = max_combined / 2;
    else if (*e1 > *e2)
        *e1 = max_combined - *e2;
    else
        *e2 = max_combined - *e1;
}

// Ensure the disambiguation popup fits inside the screen,
// clip the edges farthest to the touch point if needed.
gfx::Rect CropZoomArea(const gfx::Rect& zoom_rect,
    const gfx::Size& viewport_size,
    const gfx::Point& touch_point,
    float scale)
{
    gfx::Size max_size = viewport_size;
    max_size.Enlarge(-2 * kDisambiguationPopupBoundsMargin,
        -2 * kDisambiguationPopupBoundsMargin);
    max_size = gfx::ScaleToCeiledSize(max_size, 1.0 / scale);

    int left = touch_point.x() - zoom_rect.x();
    int right = zoom_rect.right() - touch_point.x();
    int top = touch_point.y() - zoom_rect.y();
    int bottom = zoom_rect.bottom() - touch_point.y();
    TrimEdges(&left, &right, max_size.width());
    TrimEdges(&top, &bottom, max_size.height());

    return gfx::Rect(touch_point.x() - left,
        touch_point.y() - top,
        left + right,
        top + bottom);
}

} // namespace

namespace content {

// static
float DisambiguationPopupHelper::ComputeZoomAreaAndScaleFactor(
    const gfx::Rect& tap_rect,
    const WebVector<WebRect>& target_rects,
    const gfx::Size& screen_size,
    const gfx::Size& visible_content_size,
    float total_scale,
    gfx::Rect* zoom_rect)
{
    *zoom_rect = tap_rect;
    for (size_t i = 0; i < target_rects.size(); i++)
        zoom_rect->Union(gfx::Rect(target_rects[i]));
    zoom_rect->Inset(-kDisambiguationPopupPadding, -kDisambiguationPopupPadding);

    zoom_rect->Intersect(gfx::Rect(visible_content_size));

    float new_total_scale = FindOptimalScaleFactor(target_rects, total_scale);
    *zoom_rect = CropZoomArea(
        *zoom_rect, screen_size, tap_rect.CenterPoint(), new_total_scale);

    return new_total_scale;
}

} // namespace content
